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    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        table{
            margin: 50px auto;
            border-collapse: collapse;
        }
        td{
            width: 100px;
            border: 1px solid #000;
            text-align: center;
            padding: 10px 0;
        }
    </style>
</head>
<body>
    <!-- 
        字符串拼接
        字符串 + 其他的（字符串也行）= 新的字符串

        str += '<tr>'
        str = str + '<tr>';
     -->
    <script>
        // 1、在文档中输出九九乘法表
        var str = '<table>';
        for(var i=1;i<=9;i++) {
            str+='<tr>';
            for(var j=1;j<=i;j++) {
                str+='<td>';
                str+=j+'*'+i+'='+(j*i);
                str+='</td>'
            }
            str+='</tr>'
        }
        str+='</table>';
        document.write(str);
        console.log(12345678901234565)
    </script>
</body>
</html>